president obama holding a four-point lead in this new poll, slightly outside the margin of error and significantly right at the crucial 50% mark. so the question is, what is driving the numbers in ohio right now? chief national correspondent john king has some answers. >> well, anderson, that narrow ohio lead for the president is within the poll's sampling error but it is yet another poll showing the president with a small persistent lead in the state of ohio. let's take a closer look at why it is happening in this state that is so important in the pick for president. here's the main reason right here. governor romney gets the republicans. the president gets the democrats but at the moment, in our survey, the president has a narrow lead among ohio voters who define themselves as independents. that is the battleground in a big battleground state, if you win the independents you are likely to win. governor romney close but the president with an important edge among independent voters. there's also an age divide, if you look at likely voters in ohio. among voters under the age of 50, th